As various electronic devices are down-sized and reduced in weight, a photosensitive solder resist capable of forming a fine opening pattern is being used in a printed circuit board, a semiconductor package substrate, a flexible circuit board, and the like.
A semiconductor package product is a composite material consisting of an insulator such as epoxy molding and a solder resist, a semiconductor such as a chip die, and a conductor such as a board circuit pattern, and in order to manufacture the product, various processes involving harsh thermal impact conditions should be applied.
However, since each of the insulator, the semiconductor, and the conductor has a different coefficient of thermal expansion (CTE), dimensional instability and warpage of components are generated.
Such phenomenon generates a location mismatch between a chip and a substrate when connecting a chip die and a semiconductor substrate with a solder ball or a gold wire, and also generates cracks and breakage of the product due to shear strength, which may affect the life of the product.
As the thickness of the substrate has recently become gradually thinner, such dimensional instability or warpage has become a bigger problem.
As an effort to solve this problem, a material has been developed in a direction of minimizing the CTE mismatch between materials, and a solder resist having a lower coefficient of thermal expansion is consistently required to be developed.
A previously known dry film solder resist (DFSR) has a coefficient of thermal expansion of α1 (coefficient of thermal expansion before Tg) of 45 to 70 ppm, and α2 (coefficient of thermal expansion after Tg) of 140 to 170 ppm.
Among recent substrate materials, materials having a coefficient of thermal expansion of 10 ppm or less or 5 ppm or less have been developed as a core, however, the development of the materials of the solder resist which may be used therewith is not yet known.
Further, though an attempt has been made to lower the coefficient of thermal expansion of the solder resist by increasing the content of the filler to be used, when the content of the filler is increased above a certain level, a coating defect may occur due to aggregation of the filler, and an elongation rate may be decreased after coating before curing, thereby deteriorating workability.
The solder resist is generally required to have the characteristics such as developability, a high-resolution property, an insulating property, stickiness, soldering thermal resistance, gold plating resistance, and the like.
Particularly, the solder resist for a semiconductor package substrate is, in addition to such properties, required to have, for example, crack resistance to a temperature cycle test (TCT) of −65° C. to 150° C., or a highly accelerated stress test (HAST) property between fine wires.
In recent years, as the solder resist, a dry film solder resist having good uniformity of a film thickness, surface smoothness, and thin film formability has been drawing attention.
The dry film solder resist may have an advantage in that a process for forming the resist is simplified, or a discharged amount of a solvent in the formation of the resist is reduced, in addition to the above characteristics.
Conventionally, a photocurable and thermocurable resin composition including a photopolymerizable monomer such as multifunctional acrylate, together with an acid-modified oligomer, a photoinitiator, and a thermocurable binder, has been used for forming the solder resist.
However, the solder resist formed from the resin composition does not have a high glass transition temperature, and accordingly sufficient thermal resistance reliability, and thus does not properly meet PCT resistance, TCT heat-resistance, HAST resistance between fine wires, and the like which are required for package substrate materials of a semiconductor device.
Meanwhile, due to a recent trend of lightening, thinning, shortening, and miniaturization of electronic devices and components, an integration degree of an electrical element is being increased, and a heating value of an electrical element operating with electrical energy is being greatly increased. Accordingly, there is a growing demand for improving a heat radiation property for effectively dissipating and emitting heat generated at the inside of the electronic device. In addition, as an integration degree of an electrical element is raised, an amount of generated electromagnetic waves is also increased, and these electromagnetic waves leak through a joining portion, a connecting portion, or the like of an electronic device, which lead to harmful effects such as causing a malfunction of other electrical elements or electronic components, or weakening an immune function of a human body.
Accordingly, various researches on how to simultaneously implement a heat radiation property to effectively dissipate and emit the heat generated from an electrical element, and a property to effectively shield and absorb electromagnetic waves causing a malfunction of an electrical element and having a bad influence on a human body, have been made.
Accordingly, methods of applying materials having a heat radiation property and materials for shielding and absorbing electromagnetic waves together have been suggested. Particularly, products in which a sheet having a thermal conducting property and a sheet having an electromagnetic wave shielding/absorbing performance are stacked have been widely used, but the products were thick due to the nature of the multilayered materials, had a problem in generation of an electrical short circuit and the like, and had difficulty in implementing the thermal conductivity and the electromagnetic absorbing property to the degree recently required by electronic devices. Further, in order to improve the thermal conductivity and electromagnetic absorbing property, a method of increasing a charged amount of a filler added to the multilayered materials has been suggested, however, due to compatibility and the like, it is difficult to charge the filler above a certain amount, and when the charged amount of the filler is increased, hardness of the multilayered materials is increased, thereby reducing a thermal conducting property of the product.